Long-range-ordered, hexagonally packed nanoporous membranes from degradable-block-containing diblock copolymer film templates

摘要

Polystyrene (PS)-b-polylactide (PLA) diblock copolymers with different molecular weights and fractions were synthesized through a combination of living anionic polymerization and controlled ring-opening polymerization. Then, the PS-PLA films were guided to phase-separate by self-assembly into different morphologies through casting solvent selection, solvent evaporation, and thermal and solvent-field regulation. Finally, perpendicularly oriented PS-PLA films were used as precursors for PS membranes with an ordered periodic nanoporous structure; this was achieved by the selective etching of the segregated PLA domains dispersed in a continuous matrix of PS. Testing techniques, including IR, ~1H-NMR, gel permeation chromatography, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were used to determine the chemical structure of the PS-PLA copolymer and its film morphology. AFM images of the self-assembled PS-PLA films indicate that vertical tapers of the PLA domains were generated among PS continuum when either toluene or tetrahydrofuran was used as the annealing solvent. The SEM images certified that the chemical etching of the PLA component from the self-assembled PS-PLA films led to a long-range-ordered array of hexagonally packed nanoporous membranes with a diameter about 500 nm and a center-to-center distance of 1700 nm.